Squamous cell carcinoma of unknown origin in middle mediastinum.

We report a rare case of squamous cell carcinoma located in the middle mediastinum as a solitary mass. Histologically, lymphatic tissues remained together with nests of squamous cell carcinoma which were occupying the greater part of the mass. Examinations of the whole body failed to detect a primary site of the squamous cell carcinoma. It is considered that the carcinoma cells reflect metastasis from a primary-unknown carcinoma (most likely TO lung squamous cell carcinoma) or that they originated from benign epithelial inclusions in a mediastinal lymph node.